1. Related Patent Applications
Patent application Ser. No. 876,625 by G. Davis et al, filed 6/20/86 and entitled "Digital Signal Processor With Dual CPU's Sharing Common Memory", discloses certain aspects of a digital signal processing system which can be used to implement the present invention. Parts of that application are incorporated into the following detailed description by this and subsequent references.
Patent application Ser. No. 723,991 by D. Esteban et al, filed 4/15/85 and entitled "Three Phased Pipelined Signal Processor", discloses other aspects of the digital signal processing system mentioned above pertaining to the pipelined organization of instruction execution. Parts of that application are also incorporated herein by this and subsequent references.
U.S. Pat. No. 4,899,366 by G. T. Davis et al, entitled "Tap Rotation In Fractionally Spaced Equalizer To Compensate For Drift Due To Fixed Sample Rate", discloses an equalizer scheme having particular suitability for application in modem receiver sections of the present system. The disclosure of that application is also incorporated herein by this and subsequent references.
2. Field of the Invention
This invention relates to provision of information services from digital data processing centers to diversely equipped users, through the switched public telecommunication and telephone networks, using only digital processing equipment at the centers and without dedicating equipment and/or communication circuits at such centers for adapting to the diversity of user equipment. With this invention, signals flow between the processing center and time channels of a digital carrier trunk system, such as T-1, and between the trunk system and remote users via the public network. In transit between the center and the trunk, signals are processed with all-digital modem transformations for adapting to diversity of user equipment.
The invention also concerns a digital signal processing system for interfacing between the center and trunk to perform the above-mentioned transformations in an efficient real time manner.
3. Prior Art
Digital signal processors have been used for linking multiplex communication systems operating on different parameters. U.S. Pat. No. 4,013,842 discloses an arrangement of this type in which digital signal processing is used to perform digital filtering functions between channels of time division and frequency division systems, thereby avoiding any need for down-converting signals from either system to voiceband.
Such processors have also been considered for use between single communication lines and data processing centers for transforming speech and data signals between voiceband and processable forms with benefits of reduced circuit size and cost.
However, the art does not seem to have noticed the problem presently addressed; i.e. the need for providing information communication services via the public switched network to remote users having diverse analog and digital signalling equipment, without having to dedicate circuits and equipment for matching signals sent and received by the information provider with signalling characteristics of user equipment, and without having to provide conversions of individual user signals between analog and digital forms.
What appears not to have been recognized or appreciated by those skilled in the art is that equipment and/or communication circuits need not be dedicated for such adaptation, and that equivalent effects can be obtained from all-digital equipment variably allocated in time to handle modem conversions of diverse forms on an as needed basis.
More specifically, present users of public communication networks have diverse terminal equipment for transmitting and receiving various forms of information (alphanumeric data, image data, voice, etc.) in various signal forms (e.g. speech in analog form, speech and/or modem data in log PCM digital form, data in analog form modulating sinusoidal carrier oscillations as transmitted by Bell 212A DataSet equipment, data in various digital forms associated with protocol standards such as x.21, x.25, v.24, etc.). Providers of information services (e.g. search databases) generally link to dial up subscribers either through dedicated transmission circuits and dedicated equipment associated with the type of equipment located at the user terminal, or through common equipment and variably allocated transmission circuits but with special signal form conversions performed by an intermediate carrier.
For the information provider, neither method is very efficient. Dedicated circuits and special terminal equipment to match user equipment, and/or special form conversion handling by a carrier, are costly; so costs must be passed on to the user making the information service less attractive and marketable than it otherwise could be. Dedicated circuits and equipment tend not to be occupied to capacity at all times, and are therefore inefficient. Furthermore, such arrangements are difficult to adapt to new types of service such as integrated handling of voice mail with data, or integrated handling of video conferencing services with data, etc.
Recognizing the value of and need for being able to adapt to such diverse usage of digital trunks, we have devised an adapting system and method which constitute the present invention. This system can provide not only all-digital signal form conversions of different types (through undedicated digital processing circuits), but also it can support integrated all-digital handling of voice and data and provide additional processing activities relative to data with added cost saving benefits.